1. Field of the Invention
The present invention relates to a method, an apparatus, and a program for processing information and, in particular, to a method, an apparatus, and a program that can minimize an adverse effect that occurs when a key required for decrypting stream data is encrypted and an operation for decrypting the key is not completed in time.
2. Description of the Related Art
In recent years, an encryption method has been proposed in which stream data including a plurality of successive units of data is sequentially encrypted on a unit-by-unit basis and an encryption key used for encrypting each of the units of data is changed according to a predetermined rule (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-143548).
In addition, the development of an encrypting apparatus that encrypts stream data according to such an encryption method and generates meta data including a plurality of encryption keys used for encrypting the stream data and update information for identifying the timings of updating the encryption keys has started.
Furthermore, the development of a decrypting apparatus that decrypts data encrypted using such an encrypting apparatus by using the meta data generated by the encrypting apparatus has started.
Furthermore, in order to enhance the confidentiality of these encryption keys, a technique for encrypting these encryption keys according to a second encryption method and inserting the encryption keys into meta data has been developed.
Accordingly, in this case, to decrypt each of the plurality of encryption keys encrypted according to the second method contained in the meta data, the decrypting apparatus needs to generate each of the plurality of decryption keys and carry out a decrypting operation using each of the decryption keys.